The objective of this study was to evaluate the impact of an in-service training program on nurses' performance in minimizing chemotherapy extravasation. Quasi-experimental (Pre /Posttest) research design was utilized to conduct this study. The study was conducted at the internal medical oncology departments at South Egypt Cancer Institute. A convenience sample was used to select all available nurses working in medical oncology departments (40) nurses. Data was collected by using a pre/post questionnaire sheet for nurses' knowledge, Pre/post observation checklist for nurses' practice, and an in-service nursing training program on nurses' knowledge and practice for minimizing chemotherapy extravasation. The majority of nurses have attained any training program related to chemotherapy extravasation in their last 10 years of educational and professional training, There was a Positive correlation between nurses' knowledge scores pre and post-implementation of in-service training program with ±SD mean 23.77±.97 and with P. value <0.001** There were highly statistical significant differences between total score checklist nurses' practice pre/ post implementation of in-service training program on nurses to minimize chemotherapy extravasation through mean 234.97± .15 and Value < 0.001**. The In-service training program had statistically significant improvement on totally nurses' knowledge and practice on minimizing chemotherapy extravasation.